Method for treating subsurface soils

ABSTRACT

A method is provided for increasing the stability of subsurface soils. A cavity in the subsoil is filled with a permeably consolidated aggregate and optionally clayey soils adjacent to the cavity are also treated with a clayey stabilizing chemical.

United States Patent Rosene METHOD FOR TREATING SUBSURFACE SOILS Robert B. Rosene, Tulsa, Okla.

The Dow Chemical Company, Midland, Mich.

[22] Filed: June 10,1970

[21] Appl.N0.: 45,035

[72] Inventor:

[73] Assignee:

[52] US. Cl ..6l/1l, 61/36,166/33 [51] Int. Cl. ..E02d 19/16, E02d 27/16 [58] Field ofSearch ..61/36,35,11,1, 50; 166/33, 166/292, 295; 14/33 [56] References Cited UNITED STATES PATENTS 3,386,251 6/1968 Casagrande et a1 ..6l/l l X 2,659,208 11/1953 Jourdain ..6l/ll 3,151,998 10/1964 Hemwall ..6l/36X 1,866,826 7/1932 Strothman ..61/35 X 1,355,066 10/1920 Smith ..61/11 2,767,801 10/1956 Eads ..210/170 Primary Examiner.lacob Shapiro AtIorneyGriswo1d and Burdick, Bruce M. Kanuch and William R. Norris [57] ABSTRACT A method is provided for increasing the stability of subsurface soils. A cavity in the subsoil is filled with a permeably consolidated aggregate and optionally clayey soils adjacent to the cavity are also treated with a clayey stabilizing chemical.

4 Claims, 1 Drawing Figure METHOD FOR TREATING SUBSURFACE SOILS BACKGROUND OF THE INVENTION Clayey soils (argillaceous soils) cause many problems, such as, for example, in the construction industry (under road beds, air field runways, building foundations, railroad beds and the like), where they become plastic and flowable when wetted and subjected to stresses. This phenomenon is a direct consequence of the low internal friction, bearing and shear strength of the clayey constituent of the soils. The instability of the soil causes sinking or settling of earth supported structures with cracking and subsequent disintegration thereof.

Several methods have been proposed for stabilizing such load bearing subsurface clayey soils. One method proposes to force into the soil beneath the earths surface a mobile and substantially incompressible fluid having cementitious characteristics such as taught in the method of U.S. Pat. Nos. 2,363,081 and 2,627,169.

In other methods various soil stabilizing chemicals or other materials have been added to the subsurface clayey soils in an attempt to improve their water repellency or to maintain the strength of the material when wetted. Some of these stabilizing chemicals include a mixture of orthophosphoric and sulfuric acid, lime, zirconium oxychloride (to flocculate clays), a mixture of zirconium oxychloride and a water proofing agent that will hinder the clay from imbibing moisture to the point of saturation, dihydrogenated tallow dimethyl ammonium chloride and the like. However, considerable difficulty has been encountered in providing an effective technique for disseminating the soil stabilizing chemicals and materials into the masses of the clayey soil. This difficulty is caused by the generally low permeability and fine grain nature of the soil, especially in load bearing soils (under surface structures) which have already become somewhat plastic. In one previously employed technique, a large number of holes are drilled into a clay body and the holes are filled with the treatment material. In another more recent technique (U.S. Pat. No. 3,243,962) a pressure injection method and apparatus is employed to introduce the treatment materials under pressure. In still another technique the use of electrical assistance in dewatering soils is employed. This method involves the electrical conveyance of a chemical stabilizer under a selected section of runway pavement. This was done by flowing direct current from a positive electrode to a negative electrode thereby permeating the subsoil with the stabilizer.

All of these methods, however, fail to effectively abate the problem in one aspect or another, especially where a structure already exists over the soil.

The present method proposes to solve these problems by creating an area of artificial permeability in the subsoil. This invention improves the stability of the subsoil in at least three ways: (1) structural strength is added to the subsoil area; (2) the permeability of the subsoil is increased; and (3) the mass of subsoil is made more accessible to chemical treatment.

SUMMARY OF THE INVENTION In the practice of the present invention a subsurface layer of soil is removed from a predetermined area to form a cavity. The cavity is filled with an aggregate material which is permeably consolidated by treating it with a suitable consolidating material. At this point an area of increased structural stability and permeability is established. Liquids, e.g. water, brines, etc., draining into the permeable region can be pumped or drained therefrom in any convenient manner.

As an additional step in stabilizing subsurface clayey soils a stabilizing chemical is injected through the aggregate and into the adjacent clayey subsoil.

BRIEF DESCRIPTION OF THE DRAWINGS The FIGURE is a cross-sectional view of a pavement with its load bearing subsoil material being treated according to the principals of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION The cavity in the subsoil can be created in any convenient manner. For example, a treatment bore can be sunk into the soil to a predetermined depth and then a portion of the subsoil removed from around the borehole in any convenient manner known in the art. Mechanical cutting tools and diggers can be lowered into the borehole and used to dig a horizontal cavity in the soil. Another method for creating such a cavity, which is found to be especially useful, is hydraulic jetting. This is the use of an abrasive laden fluid (carrier liquid) to cut away the subsoil. This method is commonly employed for cutting holes in casing in petroleum wells and in adjacent subterranean formations and the like. A jetting tool is employed to direct a high velocity stream of such fluid in the area desired to be cut. The tool consists of a body usually containing two or more jets aligned in a horizontal plane. The body is threaded to the end of a string of tubing which is employed to run the tool into the hole and supply the abrasive stream under pressure. The bottom of the tool is usually equipped with a ball back pressure valve. The ball can bereversed to the surface and recovered. This allows reverse circulation so that loose sand, fluid and other materials may be removed from the hole and cavity.

The jetting tool is lowered into the treatment borehole to a predetermined depth and an abrasive ladened carrier liquid is pumped through connecting tubing and through the jet at a pressure ranging up to 2,500 psi and greater. A slurry of clayey material is formed as the cavity is produced and this is pumped, or otherwise removed from the cavity. Clayey subsoils can be removed from around a borehole to a radial distance of 15 to 20 feet or more by employing this jetting method.

After the cavity is formed it is substantially completely filled with anaggregate material to form a permeable zone in the subsoil. Aggregate materials which can be employed include, for example, sand, gravel, rocks and other like hard materials which when compacted still maintain a high level of permeability. Preferably the aggregate mass has a permeability which is much greater than the clayey subsoil. Preferably the consolidated aggregate has a permeability to water of at least 10 darcies. The aggregate material is preferably treated either prior to, after or during its placement, with a consolidating material in such a manner that a permeable consolidated mass of aggregateresults. Generally, those aggregate consolidating materials employed to consolidate sand, gravel, etc. in petroleum producing and treatment wells can be employed in the method of the present invention. Plastics and other resinous materials are exemplary of treating materials which can be employed. Specific treating materials are taught in U.S. Pat. Nos. 3,199,950; 3,393,739; 3,391,738; 3,415,320; 3,419,072 (col. 1, line 56 to col. 2, line 69); the teachings of these patents being specifically incorporated herein by reference. Specific materials include by way of example, furfuryl alcohol, partial polymers of furfuryl alcohol and other compositions with furfuryl alcohol, e.g. formaldehyde, phenol-formaldehyde; thermosetting plastics which shrink when they set, epoxy resins, urea formaldehyde resins, phenolformaldehyde resins and the like. The strength and stability (to movement, etc.) of the aggregate material is increased by treating it with a consolidating material. The compressive strength required will also dictate to some degree the resin employed.

The structural stability of the clayey subsoil is greatly enhanced by the practice of the invention as defined hereinbefore. The perrneably consolidated aggregate material adds structural strength to a predetermined area while creating a permeable zone which allows the drainage of captive water from the subsoil into and through the permeable zone. The water and other liquids can be removed from the permeable zone by the use of pumps or, for example, as shown in the drawing by employing suitable drainage structures.

3,490,241, the teachings of said patent being specifically incorporated herein by reference. Other soil stabilizing chemicals include those previously described in the Background of the Invention" and many others well known in the art.

The FIGURE illustrates one embodiment of the present invention wherein a clayey load bearing subsoil located beneath a pavement 11 (a road bed or airfield strip, etc.) is treated by the method of the present invention. Three treatment boreholes l2, l3 and 14 and cavities l5, l6 and 17 are shown in the drawing. However, as many boreholes and cavities can be employed as are needed to effectively treat the sub soil condition. As shown the borehole may be extended through the road bed or air strip so that an effective area can be treated. The boreholes are first extended to a predetermined depth into the clayey subsoil. The cavities are then formed such as, for example, by a hydraulic jetting method. The cavities are then filled with a suitably treated aggregate material l8, l9 and 20, eg sand treated with a plastic, to provide an area of increased stability and permeability. As indicated previously the aggregate can be treated prior to, during and/or after its placement in the cavity. As shown in the drawing the two outside cavities are connected by conduits 21 and 22 to drainage channels 23 and 24 thereby allowing captive water in the immediate region of the treatment bores and cavities to drain off. The subsoil is optionally treated with a stabilizing material (phosphoric acid) by injecting the treating material through the boreholes and aggregate and into the surrounding clayey subsoil.

What is claimed is: i

l. A method for stabilizing clayey subsoil in a predetermined area which comprises: 7

a. preparing a cavity underground in the subsoil,

b. substantially completely filling the cavity with an aggregate which is permeably consolidated,

c. forcing through the aggregate and into the surrounding clayey subsoil a clayey soil stabilizing material, and

d. connecting said aggregate body to means for draining off liquids which flow therein.

2. A method for stabilizing load bearing clayey subsoil which comprises:

a. sinking a treatment borehole into said subsoil;

b. forming a cavity adjacent to said borehole at a predetermined depth in the subsoil;

c. filling the cavity with a permeably consolidated aggregate; and

d. treating the clayey soil surrounding the cavity with a chemical stabilizing agent.

3. In the method of strengthening a subsurface formation containing water sensitive clay minerals consisting of placing a permeable aggregate mass in certain areas of said formation to provide both a non-water sensitive mass and a means for draining liquids from a portion of said formation the improvement which comprises:

a. treating at least a portion of the formation surrounding said aggregate mass with a stabilizer for said clay minerals to render said minerals less sensitive to water, and

b. permeably consolidating said aggregate mass.

4. The method of claim 3 including in addition providing drainage means connected to said aggregate mass for draining liquids therefrom. 

2. A method for stabilizing load bearing clayey subsoil which comprises: a. sinking a treatment borehole into said subsoil; b. forming a cavity adjacent to said borehole at a predetermined depth in the subsoil; c. filling the cavity with a permeably consolidated aggregate; anD d. treating the clayey soil surrounding the cavity with a chemical stabilizing agent.
 3. In the method of strengthening a subsurface formation containing water sensitive clay minerals consisting of placing a permeable aggregate mass in certain areas of said formation to provide both a non-water sensitive mass and a means for draining liquids from a portion of said formation the improvement which comprises: a. treating at least a portion of the formation surrounding said aggregate mass with a stabilizer for said clay minerals to render said minerals less sensitive to water, and b. permeably consolidating said aggregate mass.
 4. The method of claim 3 including in addition providing drainage means connected to said aggregate mass for draining liquids therefrom. 